1. Field of the Invention
The present invention relates to a boiling cooling system that exchanges heat between a higher-temperature fluid and a lower-temperature fluid through boiling heat transfer of a refrigerant that is sealingly contained within the boiling cooling system.
2. Description of Related Art
For instance, when it is required to cool an interior of a substantially airtight housing, such as a housing of a base station of a cellular phone system, the interior of the housing cannot be cooled by directly introducing external air into the interior of the housing. In such a case, a boiling cooling system may be used to exchange heat between internal air located within the housing and the external air located outside of the housing to cool the interior of the housing.
As shown in FIG. 6, one previously proposed type of boiling cooling system includes a first heat exchanging unit 110 located inside of a housing 100 and a second heat exchanging unit 120 located outside of the housing 100. The first heat exchanging unit 110 is communicated with the second heat exchanging unit 120 through pipes 130 to circulate a refrigerant, which is sealingly contained in the boiling cooling system, between the first heat exchanging unit 110 and the second heat exchanging unit 120. In the boiling cooling system, the liquid state refrigerant contained in the first heat exchanging unit 110 takes heat from higher-temperature air (hot air) contained within the housing 100 and vaporizes. Then, the transformed vapor state refrigerant in the first heat exchanging unit 110 flows into the second heat exchanging unit 120 through one of the pipes 130. In the second heat exchanging unit 120, the vapor state refrigerant radiates heat into external air or lower-temperature air located outside of the housing 100 through the second heat exchanging unit 120 and condenses into the liquid. Then, the liquid state refrigerant in the second heat exchanging unit 120 is returned into the first heat exchanging unit 110 through the other one of the pipes 130. In this manner, the heat is transferred from the higher-temperature air located within the housing 100 to the lower-temperature air located outside of the housing 100. Thus, the rise of the temperature of the internal air located within the housing 100 is restrained.
When the liquid state refrigerant starts boiling in the first heat exchanging unit 110, a pressure difference is created between the first heat exchanging unit 110 and the second heat exchanging unit 120 in the boiling cooling system. As the pressure difference is created, a fluid level of the liquid state refrigerant in the higher pressure side, i.e., in the first heat exchanging unit 110 drops while a fluid level of the liquid state refrigerant in the lower pressure side, i.e., in the second heat exchanging unit 120 rises. At this stage, when the fluid level of the liquid state refrigerant in the lower pressure side, i.e., in the second heat exchanging unit 120 rises, the liquid state refrigerant occupies a lower portion of a heat radiating core of the second heat exchanging unit 120. Thus, an effective heat radiating surface area of the second heat exchanging unit 120 decreases, resulting in a decrease in a heat radiating performance. To address this disadvantage, in the previously proposed boiling cooling system, an upper tank 111 of the first heat exchanging unit 110 is positioned below and is spaced apart from a lower tank 121 of the second heat exchanging unit 120 in such a manner that a vertical space corresponding to the pressure difference (head difference) H between the higher pressure side and the lower pressure side is provided between the upper tank 111 of the first heat exchanging unit 111 and the lower tank 121 of the second heat exchanging unit 120, as shown in FIG. 6. Because of the vertical space corresponding to the head difference H, the liquid state refrigerant does not reach the heat radiating core of the second heat exchanging unit 120, so that the required heat radiating performance of the second heat exchanging unit 120 is maintained during the operation of the boiling cooling system.
However, in such a boiling cooling system, in order to further improve the heat radiating performance of the second heat exchanging unit 120 without modifying the vertical space corresponding to the head difference H, a vertical size of the second heat exchanging unit 120 needs to be increased. This causes a disadvantageous increase in an entire vertical size of the boiling cooling system.
The present invention addresses the above disadvantages. Thus, it is an objective of the present invention to provide a boiling cooling system that has an improved heat radiating performance without substantially increasing a size of the boiling cooling system.
To achieve the objective of the present invention, there is provided a boiling cooling system that exchanges heat between a higher-temperature fluid and a lower-temperature fluid through boiling heat transfer of a refrigerant sealingly contained within the boiling cooling system. The boiling cooling system includes a first heat exchanging unit, a second heat exchanging unit, a vapor transfer pipe and a liquid return pipe.
The first heat exchanging unit includes a boiling core and an upper tank. The boiling core exchanges heat between the higher-temperature fluid and the refrigerant upon exposure to the higher-temperature fluid. The upper tank is arranged above the boiling core and fluidly communicates with the boiling core.
The second heat exchanging unit includes a heat radiating core and a lower tank. The heat radiating core exchanges heat between the lower-temperature fluid and the refrigerant upon exposure to the lower-temperature fluid. The lower tank is arranged below the heat radiating core and fluidly communicates with the heat radiating core.
The vapor transfer pipe communicates the first heat exchanging unit with the second heat exchanging unit to conduct the refrigerant in a vapor state. The refrigerant is transformed into the vapor state within the first heat exchanging unit upon absorbing heat from the higher-temperature fluid. The refrigerant in the vapor state in the first heat exchanging unit flows to the second heat exchanging unit through the vapor transfer pipe.
The liquid return pipe communicates the second heat exchanging unit with the first heat exchanging unit to conduct the refrigerant in a liquid state. The refrigerant is transformed into the liquid state within the second heat exchanging unit upon radiating heat into the lower-temperature fluid. The refrigerant in the liquid state in the second heat exchanging unit flows to the first heat exchanging unit through the liquid return pipe.
The upper tank of the first heat exchanging unit is arranged at generally the same height as that of the lower tank of the second heat exchanging unit. An upstream end of the vapor transfer pipe is connected to the upper tank of the first heat exchanging unit. An upstream end of the liquid return pipe is connected to the lower tank of the second heat exchanging unit. The refrigerant in the liquid state generally fills up to a top of an interior space of the upper tank of the first heat exchanging unit and also generally fills up to a top of an interior space of the lower tank of the second heat exchanging unit while the boiling cooling system is not operated.